Semiconductor light emitting device with light transmittable electrode and method for manufacturing same

ABSTRACT

According to one embodiment, a semiconductor light emitting device includes first and second conductive layers, a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and a light emitting part. The second semiconductor layer is provided between the first conductive layer and the first semiconductor layer. The light emitting part is provided between the first and second semiconductor layers. The second conductive layer is in contact with the second semiconductor layer and the first conductive layer between the second semiconductor layer and the first conductive layer. The first and second conductive layers are transmittable to light emitted from the light emitting part. The first conductive layer includes a polycrystal having a first average grain diameter. The second conductive layer includes a polycrystal having a second average grain diameter of 150 nanometers or less and smaller than the first average grain diameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2011-14117, filed on Jan. 26,2011; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor lightemitting device and a method for manufacturing the same.

BACKGROUND

In recent years, research and development of a blue or green lightemitting diode using a GaN-based semiconductor have been proceeding. Inan FU (Face UP) type light emitting diode, that is, one with a structurein which light is extracted from the opposite side of a growthsubstrate, for example, ITO (Indium Tin Oxide) is used as a conductivelayer on a p-type GaN contact layer. Such a conductive layer is requiredto be excellent in the electrical characteristics, such as volumeresistivity and contact resistance, and excellent in processability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating the configuration of asemiconductor light emitting device according to an embodiment;

FIGS. 2A to 2C are schematic sectional views illustrating theconfiguration of a part of the semiconductor light emitting deviceaccording to the embodiment;

FIGS. 3A to 3C are schematic sectional views illustrating theconfiguration of a part of the semiconductor light emitting deviceaccording to the embodiment;

FIGS. 4A to 4C are microscopic photo images of the transparentconductive film;

FIGS. 5A to 5C are graphs illustrating the characteristics of thesemiconductor light emitting device;

FIG. 6 is a graph illustrating the characteristics of the semiconductorlight emitting device according to the embodiment;

FIG. 7 is a flowchart illustrating a method of manufacturing thesemiconductor light emitting device according to the embodiment;

FIGS. 8A to 8C are schematic sectional views in order of process,illustrating the method of manufacturing the semiconductor lightemitting device according to the embodiment;

FIG. 9 is a schematic sectional view illustrating the configuration ofanother semiconductor light emitting device according to the embodiment;and

FIG. 10 is a schematic sectional view illustrating the configuration ofstill another semiconductor light emitting device according to theembodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor light emittingdevice includes a first conductive layer, a first semiconductor layer ofa first conductivity type, a second semiconductor layer of a secondconductivity type, a light emitting part, and a second conductive layer.The second semiconductor layer is provided between the first conductivelayer and the first semiconductor layer. The light emitting part isprovided between the first semiconductor layer and the secondsemiconductor layer. The second conductive layer is in contact with thesecond semiconductor layer and with the first conductive layer betweenthe second semiconductor layer and the first conductive layer. The firstconductive layer includes a polycrystal having a first average graindiameter. The first conductive layer is transmittable with respect tolight emitted from the light emitting part. The second conductive layerincludes a polycrystal having a second average grain diameter of 150nanometers or less. The second average grain diameter is smaller thanthe first average grain diameter, and the second conductive layer istransmittable with respect to the light.

In general, according to another embodiment, a method of manufacturing asemiconductor light emitting device is disclosed. The semiconductorlight emitting device includes a first conductive layer, a firstsemiconductor layer of a first conductivity type, a second semiconductorlayer of a second conductivity type, a light emitting part, and a secondconductive layer. The second semiconductor layer is provided between thefirst conductive layer and the first semiconductor layer. The lightemitting part is provided between the first semiconductor layer and thesecond semiconductor layer. The second conductive layer is in contactwith the second semiconductor layer and with the first conductive layerbetween the second semiconductor layer and the first conductive layer.The first conductive layer includes a polycrystal having a first averagegrain diameter. The first conductive layer is transmittable with respectto light emitted from the light emitting part. The second conductivelayer includes a polycrystal having a second average grain diametersmaller than the first average grain diameter. The second conductivelayer is transmittable with respect to the light. The method can includeforming a first film serving as the second conductive layer on thesecond semiconductor layer in an atmosphere of a noble gas by asputtering method using a first electric power. The method can includeforming a second film serving as the first conductive layer on the firstfilm in an atmosphere of a noble gas by the sputtering method using asecond electric power smaller than the first electric power. Inaddition, the method can include forming the first conductive layer andthe second conductive layer by subjecting the first film and the secondfilm to a heat treatment in an atmosphere including oxygen.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

The drawings are schematic or conceptual; and the relationships betweenthe thicknesses and widths of portions, the proportions of sizes amongportions, etc., are not necessarily the same as the actual valuesthereof. Further, the dimensions and the proportions may be illustrateddifferently among the drawings, even for identical portions.

In the application and the drawings of the application, componentssimilar to those described in regard to a drawing thereinabove aremarked with like reference numerals, and a detailed description isomitted as appropriate.

Embodiment

FIG. 1 is a schematic sectional view illustrating the configuration of asemiconductor light emitting device according to an embodiment.

As shown in FIG. 1, a semiconductor light emitting device 110 accordingto the embodiment includes a first semiconductor layer 10 of a firstconductivity type, a second semiconductor layer 20 of a secondconductivity type, a light emitting part 30, a first conductive layer51, and a second conductive layer 52.

The second semiconductor layer 20 is provided between the firstconductive layer 51 and the semiconductor layer 20.

The light emitting part 30 is provided between the first semiconductorlayer 10 and the second semiconductor layer 20. The first conductivelayer 51 includes a polycrystal. The first conductive layer 51 istransmittable to light emitted from the light emitting part 30.

The second conductive layer 52 is in contact with the secondsemiconductor layer 20 and the first conductive layer 51 between thesecond semiconductor layer 20 and the first conductive layer 51. Thesecond conductive layer 52 includes a polycrystal. The second conductivelayer 52 is transmittable to the above-mentioned light.

That is, the light emitting part 30 is provided on the firstsemiconductor layer 10. The second semiconductor layer 20 is provided onthe light emitting part 30. The second conductive layer 52 is providedon the second semiconductor layer 20. The first conductive layer 51 isprovided on the second conductive layer 52.

The first conductive layer 51 and the second conductive layer 52 areincluded in a transparent electrode 50.

For example, the first conductivity type is an n-type and the secondconductivity type is a p-type. However, the embodiment is not limited tothe above and the first conductivity type may be a p-type and the secondconductivity type may be an n-type. Hereinafter, explanation is given onthe assumption that the first conductivity type is an n-type and thesecond conductivity type is a p-type.

Here, it is assumed that a direction from the first semiconductor layer10 toward the second semiconductor layer 20 is a Z-axis (first axis).One axis perpendicular to the Z-axis is assumed to be an X-axis (secondaxis). An axis perpendicular to the Z-axis and the X-axis is assumed tobe a Y-axis (third axis).

The first semiconductor layer 10, the second semiconductor layer 20, andthe light emitting part 30 include, for example, a nitridesemiconductor.

As shown in FIG. 1, the semiconductor light emitting device 110 canfurther include a substrate 5 and a buffer layer 6. The firstsemiconductor layer 10 is arranged between the substrate 5 and the lightemitting part 30. The buffer layer 6 is arranged between the substrate 5and the first semiconductor layer 10.

As the substrate 5, a substrate made up of, for example, sapphire isused. A major surface of the substrate 5 is referred to as a (0001)surface, that is, a c surface. The major surface of the substrate 5 maybe inclined at an angle of, for example, 5 degrees or less with respectto the (0001) surface. As the buffer layer 6, for example, anAl_(x0)Ga_(1-x0)N (0≦x0≦1) layer is used.

The first semiconductor layer 10 includes, for example, a first n-sidelayer 11 and a second n-side layer 12. The second n-side layer 12 isprovided between the first n-side layer 11 and the light emitting part30. The first n-side layer 11 functions as an n-type contact layer. Thesecond n-side layer 12 functions as an n-type guide layer. As the firstn-side layer 11, a GaN layer, for example, to which n-type impurities(for example, silicon etc.) are added in a high concentration, is used.As the second n-side layer 12, a GaN layer etc., to which n-typeimpurities are added in, for example, a concentration lower than that ofthe first n-side layer 11, is used.

The second semiconductor layer 20 includes a first p-side layer 21 and asecond p-side layer 22. The first p-side layer 21 is provided betweenthe second p-side layer 22 and the light emitting part 30. The firstp-side layer 21 functions as, for example, an electron overflowprevention layer (suppression layer). The second p-side layer 22functions as a p-type contact layer. As the first p-side layer 21, anAlGaN layer etc., to which p-type impurities (for example, magnesium)are added, is used. As the second p-side layer 22, a GaN layer etc., towhich p-type impurities are added in a high concentration, is used.

The semiconductor light emitting device 110 further includes a firstelectrode 70 and a second electrode 80. The first electrode 70 iselectrically connected to the first semiconductor layer 10(specifically, the first n-side layer 11, which is an n-type contactlayer). The second electrode 80 is electrically connected to, forexample, the transparent electrode 50.

The second electrode 80 is electrically connected to the secondsemiconductor layer 20 (specifically, the second p-side layer 22, whichis a p-type contact layer) via the transparent electrode 50.

In the specific example, the second electrode 80 is provided on thetransparent electrode 50 (specifically, the first conductive layer 51)provided on the second semiconductor layer 20 (specifically, the secondp-side layer 22, which is a p-side contact layer).

As the first electrode 70, for example, a stacked film of a Ti film, Ptfilm, and Au film is used. As the second electrode 80, for example, astacked film of a Ni film and Au film is used.

By a voltage applied between the first electrode 70 and the secondelectrode 80, an electric current is supplied to the light emitting part30 via the first semiconductor layer 10, the second semiconductor layer20 and the transparent electrode 50, and light (emission light) isemitted from the light emitting part 30.

The light emitting part 30 emits at least any of ultraviolet, purple,blue, and green light. That is, the wavelength (major wavelength) ofemission light emitted from the light emitting part 30 is 360 nm or moreand 580 nm or less.

A stacked structure body 10 s includes the first semiconductor layer 10,the second semiconductor layer 20, and the light emitting part 30. Inthe specific example, on a first major surface 10 a on the side of thesecond semiconductor layer 20 of the stacked structure body 10 s, a partof the first semiconductor layer 10, a part of the light emitting part30, and a part of the second semiconductor layer 20 are removed.

The stacked structure body 10 s has the first major surface 10 a on theside of the second semiconductor layer 20 and a second major surface 10b on the side of the first semiconductor layer 10. The second majorsurface 10 b is a surface on the opposite side of the first majorsurface 10 a in the stacked structure body 10 s. The first semiconductorlayer 10 is exposed on the first major surface 10 a of the stackedstructure body 10 s.

That is, the light emitting part 30 is provided between a part of thefirst semiconductor layer 10 and the second semiconductor layer 20. Onthe side of the first major surface 10 a, the first electrode 70 isprovided in contact with the first semiconductor layer 10. On the sideof the second major surface 10 b, the second electrode 80 is provided incontact with the transparent electrode 50 contacting the secondsemiconductor layer 20. On the second major surface 10 b of the stackedstructure body 10 s, the substrate 5 and the buffer layer 6 areprovided.

The light emitting part 30 has a single quantum well (SQW) structure ora multi quantum well (MQW) structure.

FIGS. 2A to 2C are schematic sectional views illustrating theconfiguration of a part of the semiconductor light emitting deviceaccording to the embodiment.

That is, these figures are schematic views illustrating an example ofthe configuration of the light emitting part 30.

As shown in FIG. 2A, in a semiconductor light emitting device 100 aaccording to the embodiment, the light emitting part 30 has the SQWstructure. That is, the light emitting part 30 includes a barrier layerBL (first barrier layer BL1), a p-side barrier layer BLp, and a welllayer WL (first well layer WL1) provided between the first barrier layerBL1 and the p-side barrier layer BLp.

It is noted that in the specification of the application, the “stackedlayer” includes a case where another layer is inserted and stacked, inaddition to a case where layers are stacked directly. For example, aswill be described later, another layer may be provided between the firstbarrier layer BL1 and the first well layer WL1 and between the firstwell layer WL1 and the p-side barrier layer BLp.

As shown in FIG. 2B, in a semiconductor light emitting device 100 baccording to the embodiment, the light emitting part 30 has the MQWstructure. That is, the light emitting part 30 includes a plurality ofbarrier layers (in the example, the first to fourth barrier layers BL1to BL4 and the p-side barrier layer BLp) stacked along the Z-axis andwell layers (the first to fourth well layers WL1 to WL4) providedbetween each of the plurality of barrier layers. In the specificexample, four well layers are provided, but the number of well layers isarbitrary.

As described above, the light emitting part 30 further includes an N-thbarrier layer provided on the opposite side of an (N−1)th barrier layerof an (N−1)th well layer WL and an N-th well layer provided on theopposite side of the (N−1)th well layer of the N-th barrier layer, whereN is an integer of two or more.

As shown in FIG. 2C, in a semiconductor light emitting device 110 caccording to the embodiment, the light emitting part 30 further includesan intermediate layer provided in each of regions between the barrierlayers and the well layers, respectively. That is, the light emittingpart 30 further includes a first intermediate layer IL1 provided betweenthe (N−1)th barrier layer and the (N−1)th well layer and a secondintermediate layer IL2 provided between the (N−1)th well layer and theN-th barrier layer. Furthermore, the second intermediate layer IL2 isprovided between the N-th well layer and the p-side barrier layer BLp.The first intermediate layer IL1 and the second intermediate layer IL2are provided as necessary and can be omitted. Moreover, it may also bepossible to provide the first intermediate layer IL1 and omit the secondintermediate layer IL2. Alternatively, it may also be possible toprovide the second intermediate layer IL2 and omit the firstintermediate layer IL1.

As the barrier layer (for example, the first to fourth barrier layersBL1 to BL4, the N-th barrier layer), for example,In_(x1)Al_(y1)Ga_(1-x1-y1)N (0≦x1≦1, 0≦y1<1, x1+y1≦1) can be used. Asthe barrier layer, for example, In_(0.02)Al_(0.33)Ga_(0.65)N can beused. The thickness of the barrier layer can be set to, for example,12.5 nm.

As the p-side barrier layer BLp, for example,In_(x2)Al_(y2)Ga_(1-x2-y2)N (0≦x2<1, 0≦y2<1, x2+y2≦1) can be used. Asthe p-side barrier layer BLp, for example, In_(0.02)Al_(0.33)Ga_(0.65)Ncan be used. The thickness of the barrier layer can be set to, forexample, 12.5 nm.

As the well layer (for example, the first well layer WL1 to WL4, theN-th well layer), for example, In_(x3)Al_(y3)Ga_(1-x3-y3)N (0≦x3<1,0≦y3<1, x3+y3≦1) can be used. As the well layer, for example,In_(0.15)Ga_(0.85)N can be used. The thickness of the well layer can beset to, for example, 2.5 nm.

The composition ratio of In included in the well layer (ratio of thenumber of In atoms in the group III elements) is higher than thecomposition ratio of In included in the barrier layer (the first tofourth barrier layers BL1 to BL4, the N-th barrier layer, and the p-sidebarrier layer BLp) (ratio of the number of In atoms in the group IIIelements). This makes the band gap energy in the barrier layer greaterthan the band gap energy in the well layer.

As the first intermediate layer IL1, for example, In_(x4)Ga_(1-x4)N(0≦x4<1) can be used. As the first intermediate layer IL1, for example,In_(0.02)Ga_(0.98)N can be used. The thickness of the first intermediatelayer IL1 can be set to, for example, 0.5 nm.

As the second intermediate layer IL2, for example, In_(x5)Ga_(1-x5)N(0≦x5<1) can be used. As the second intermediate layer IL2, for example,In_(0.02)Ga_(0.98)N can be used. The thickness of the secondintermediate layer IL2 can be set to, for example, 0.5 nm.

It is noted that the composition ratio of In included in the well layer(ratio of the number of In atoms in the group III elements) is higherthan the composition ratio of In included in the first intermediatelayer IL1 and the second intermediate layer IL2 (ratio of the number ofIn atoms in the group III elements). This makes the band gap energy inthe first intermediate layer IL1 and the second intermediate layer IL2greater than the band gap energy in the well layer.

It is noted that it is possible to regard the first intermediate layerIL1 as a part of the barrier layer. Furthermore, it is also possible toregard the second intermediate layer IL2 as a part of the barrier layer.That is, the barrier layer stacked with the well layer may include aplurality of layers of different compositions.

It is noted that in the SQW structure illustrated in FIG. 2A, the firstintermediate layer IL1 and the second intermediate layer IL2 may beprovided. In this case, the first intermediate layer IL1 is providedbetween the first barrier layer BL1 and the first well layer WL1, andthe second intermediate layer IL2 is provided between the first welllayer WL1 and the p-side barrier layer BLp.

The above is an example of the configuration of the light emitting part30, but the embodiment is not limited to this and there can be variousmodifications of the materials used for the barrier layer, the p-sidebarrier layer BLp, the well layer, the first intermediate layer IL1, andthe second intermediate layer IL2 and their thicknesses. It is notedthat as described above, the barrier layer, the p-side barrier layerBLp, the well layer, the first intermediate layer IL1, and the secondintermediate layer IL2 include a nitride semiconductor.

Hereinafter, the configuration and characteristics of the transparentelectrode 50 are described by taking the semiconductor light emittingdevice 110 as an example. The following description is applied to asemiconductor light emitting device having various configurations, suchas the semiconductor light emitting devices 110 a, 110 b, and 110 c.

The first conductive layer 51 and the second conductive layer 52includes an oxide including at least one (kind of) element selected fromthe group of In, Sn, Zn, and Ti. As the first conductive layer 51 andthe second conductive layer 52, for example, ITO is used. As the firstconductive layer 51 and the second conductive layer 52, at least any of,for example, In₂O₃ and SnO₂ may be used.

As already described above, the first conductive layer 51 and the secondconductive layer 52 include a polycrystal. That is, as the firstconductive layer 51 and the second conductive layer 52, apolycrystalline film including a metal oxide is used. Here, in thepolycrystal (polycrystalline film), a plurality of diffraction peaks areobserved by X-ray diffraction measurement. It is noted that in theamorphousness (amorphous film), the sharp diffraction peak is notobserved by the observation in the X-ray diffraction measurement but abroad halo peak is observed.

FIGS. 3A to 3C are schematic sectional views illustrating theconfiguration of a part of the semiconductor light emitting deviceaccording to the embodiment.

FIG. 3A is a sectional view when a part of the semiconductor lightemitting device 110 is cut in a plane parallel to the Z-axis. FIG. 3B isa plan view schematically showing the configuration of the firstconductive layer 51 when the first conductive layer 51 is viewed alongthe Z-axis. FIG. 3C is a plan view schematically showing theconfiguration of the second conductive layer 52 when the secondconductive layer 52 is viewed along the Z-axis.

As shown in FIG. 3A, the first conductive layer 51 includes a pluralityof grains (plurality of first grains 51 g). A grain boundary (firstgrain boundary 51 gb) is provided between the plurality of the firstgrains 51 g. That is, a region between the first grain boundaries 51 gbforms the first grain 51 g.

The second conductive layer 52 includes a plurality of grains (pluralityof first grains 52 g). A grain boundary (second grain boundary 52 gb) isprovided between the plurality of the second grains 52 g. That is, aregion between the second grain boundaries 52 gb forms the second grain52 g.

The diameter of the first grain 51 g is greater than that of the secondgrain 52 g.

The shape of such a grain is found based on, for example, a transmissionelectron microscopic image.

For example, the diameter of the first grain 51 g at the center alongthe axis (Z-axis) in the direction of the thickness of the firstconductive layer 51 (diameter along the axis perpendicular to theZ-axis) is greater than the diameter of the second grain 52 g at thecenter along the axis (Z-axis) in the direction of the thickness of thesecond conductive layer 52 (diameter along the axis perpendicular to theZ-axis).

For example, the plurality of the first grains 51 g have a first averagegrain diameter d1. The first average grain diameter d1 is, for example,an average of diameters of the plurality of the first grains 51 g at thecenter along the Z-axis of the first conductive layer 51. The firstaverage grain diameter d1 is, for example, an average of diametersalong, for example, the X-axis (or Y-axis) of the plurality of the firstgrains 51 g at the center along the Z-axis of the first conductive layer51.

For example, the plurality of the second grains 52 g have a secondaverage grain diameter d2. The second average grain diameter d2 is, forexample, an average of diameters of the plurality of the second grains52 g at the center along the Z-axis of the second conductive layer 52.The second average grain diameter d2 is, for example, an average ofdiameters along, for example, the X-axis (or Y-axis) of the plurality ofthe second grains 52 g at the center along the Z-axis of the secondconductive layer 52.

The first average grain diameter d1 is greater than the second averagegrain diameter d2.

As shown in FIG. 3A, the first conductive layer 51 has a first surface51 a on the side of the second conductive layer 52 and a second surface51 b on the opposite side of the second conductive layer 52.Furthermore, the second conductive layer has a third surface 52 a on theside of the second semiconductor layer 20 and a fourth surface 52 b onthe side of the first conductive layer 51.

As the first average grain diameter d1, for example, an average ofdiameters of the plurality of the first grains 51 g on the first surface51 a may be used. As the first average grain diameter d1, for example,an average of diameters of the plurality of the first grains 51 g on thesecond surface 51 b may be used.

As the second average grain diameter d2, for example, an average ofdiameters of the plurality of the second grains 51 g on the thirdsurface 52 a may be used. As the second average grain diameter d2, forexample, an average of diameters of the plurality of the second grains51 g on the fourth surface 52 b may be used.

In this case also, the first average grain diameter d1 is greater thanthe second average grain diameter d2.

FIG. 3B illustrates the plurality of the first grains 51 g on the secondsurface 51 b. As shown in FIG. 3B, the shapes of the plurality of thefirst grains 51 g differ from one another.

FIG. 3C illustrates the plurality of the second grains 52 g on thefourth surface 52 b. As shown in FIG. 3C, the shapes of the plurality ofthe second grains 52 g differ from one another.

When the grain has an elongated shape, the diameter of the grain isdetermined as the length of the grain along an axis in the direction ofthe longer diameter. That is, the maximum value of the diameter of eachof the grains is determined as the diameter of the grain. Then, anaverage of the diameters of the plurality of grains is determined as anaverage diameter (the first average grain diameter d1 or the secondaverage grain diameter d2).

When the first average grain diameter d1 and the second average graindiameter d2 are found quantitatively, the values described in FIG. 3Aare used. That is, the first average grain diameter d1 is an average ofdiameters of the plurality of the first grains 51 g at the center alongthe Z-axis of the first conductive layer 51. Then, the second averagegrain diameter d2 is an average of diameters of the plurality of thesecond grains 52 g at the center along the Z-axis of the secondconductive layer 52.

In the semiconductor light emitting device 110 according to theembodiment, the second average grain diameter d2 is smaller than thefirst average grain diameter d1 and is 150 nm or less. That is, thesecond conductive layer 52 includes a polycrystal having the secondaverage grain diameter d2, which is smaller than the first average graindiameter d1 and is 150 nm or less.

Because of the above, it is possible to provide a semiconductor lightemitting device excellent in electrical characteristics andprocessability.

The thickness of the second conductive layer 52 (thickness along theZ-axis) is less than that of the first conductive layer 51 (thicknessalong the Z-axis).

As will be described later, the first conductive layer 51 and the secondconductive layer 52 can be formed by the vapor phase epitaxy method. Forexample, the first conductive layer 51 and the second conductive layer52 can be formed by the sputtering method.

The second average grain diameter d2 in the second conductive layer 52provided on the second semiconductor layer 20 is small. Thus excellentelectrical characteristics are obtained between the second conductivelayer 52 and the second semiconductor layer 20. That is, the contactresistance between the second conductive layer 52 and the secondsemiconductor layer 20 is low.

On the other hand, as described already, the thickness of the secondconductive layer 52 is less than that of the first conductive layer 51.Thus, the second average grain diameter d2 in the second conductivelayer 52 is smaller than the first average grain diameter d1 in thefirst conductive layer 51, and then, excellent processability can besecured in the second conductive layer 52 even if the processability ofthe material of the second conductive layer 52 is low.

The thickness of the second conductive layer 52 is, for example, 100 nmor less. This makes it easy to obtain excellent processability of thesecond conductive layer 52. It is more desirable for the thickness ofthe second conductive layer 52 to be 50 nm or less. Thus, more excellentprocessability can be obtained.

On the other hand, the thickness of the first conductive layer 51 can bedetermined from the viewpoint of the electrical characteristics and theoptical characteristics.

That is, if the thickness of the first conductive layer 51 is extremelysmall, the resistance of the transparent electrode 50 becomes too high.Furthermore, the thickness of the transparent electrode 50 (the totalthickness of the first conductive layer 51 and the second conductivelayer 52) is set so that the transmittance of the transparent electrode50 is high. A relationship between thickness and transmittance of thetransparent electrode 50 will be described later.

Hereinafter, the result of an experiment on a relationship between thegrain diameter of a transparent conductive film that forms thetransparent electrode 50, the contact resistance, and the processabilitywill be described. In the experiment, an ITO film was formed as atransparent conductive film on the second semiconductor layer 20. Atthis time, specimens of the ITO films the thicknesses of which aredifferent were manufactured.

In the formation of the transparent conductive film, a target of ITO wasused and an inert gas atmosphere substantially not including oxygen wasused. Immediately after the transparent conductive film is formed, thetransparent conductive film is, for example, amorphous. Alternatively,immediately after the transparent conductive film is formed, thetransparent conductive film is, for example, in a state where anamorphous portion and a polycrystalline portion are mixed.

After forming the transparent conductive film, the transparentconductive film was processed into a predetermined shape. Then, theresidue at the time of the processing was evaluated by observing thelevel of residue using an optical microscope or a scanning electronmicroscope.

After that, the transparent conductive film was subjected to heattreatment. This causes the transparent conductive film to be into apolycrystalline state. The heat treatment was performed under thecondition of presence of oxygen. Specifically, the heat treatment wasperformed in an atmosphere including air.

By changing the sputtering conditions for formation of the transparentconductive film, the grain diameter in the transparent conductive filmafter the heat treatment changes. Specifically, in the experiment,electric power used at the time of sputtering was changed when formingthe transparent conductive film.

Then, the grain diameter of the transparent conductive film after theheat treatment was measured. Furthermore, after the heat treatment, thecontact resistance between the transparent conductive film and thesecond semiconductor layer 20 was measured.

FIGS. 4A to 4C are microscopic photo images of the transparentconductive film.

FIGS. 4A to 4C correspond to first to third specimens SP1 to SP3,respectively. For the first to third specimens SP1 to SP3, electricpower at the time of sputtering is different. As shown in these Figures,the buffer layer 6 and the second semiconductor layer 20 (GaN layer) areformed sequentially on the sapphire substrate 5 and a transparentconductive film 50 f is formed further thereon. In these Figures, agrain boundary 50 gb of the transparent conductive film 50 f is shown byan arrow.

As shown in FIG. 4A, in the first specimen SP1, the intervals betweenthe grain boundaries 50 gb are narrow. The average grain diameter in thefirst specimen SP1 is 134 nm.

As shown in FIG. 4B, in the second specimen SP2, the intervals betweenthe grain boundaries 50 gb are wider than those in the first specimenSP1. The average grain diameter in the second specimen SP2 is 150 nm.

As shown in FIG. 4C, in the third specimen SP3, the intervals betweenthe grain boundaries 50 gb are wider than those in the second specimenSP2. The average grain diameter in the third specimen SP3 is 224 nm.

As described above, it is possible to control the average grain diameterof the transparent conductive film 50 f by the manufacturing conditions.

FIGS. 5A to 5C are graphs illustrating the characteristics of thesemiconductor light emitting device.

FIG. 5A shows a relationship between a contact resistance R1 between thetransparent conductive film and the second semiconductor layer 20 and agrain diameter d of the transparent conductive film. In FIG. 5A, thecontact resistance R1 is expressed by relative values. FIG. 5B shows arelationship between a processability index PA of the transparentconductive film and the grain diameter d of the transparent conductivefilm. Here, the grain diameter d is an average diameter of a pluralityof grains in the transparent conductive film. A case where theprocessability index PA is 1 corresponds to a case where the residue ishardly observed. Then, the greater the processability index PA, the morethe residue exists. It is desirable for the processability index PA tobe small. FIG. 5C shows a relationship between the processability indexPA of the transparent conductive film and a thickness t of thetransparent conductive film.

As shown in FIG. 5A, when the grain diameter d of the transparentconductive film is great, the contact resistance R1 is high. When thegrain diameter d is small, the contact resistance R1 is low. From thisresult, it is desirable for the grain diameter d to be small from theviewpoint of the contact resistance R1. In particular, when the graindiameter d is 150 nm or less, the effect of reduction in the contactresistance R1 becomes remarkable.

As shown in FIG. 5B, when the grain diameter d of the transparentconductive film is great, the processability index PA is small and theresidue is little. When the grain diameter d is small, theprocessability index PA is great, that is, the residue is much.

As shown in FIG. 5B, the smaller the thickness t of the transparentconductive film, the smaller the processability index PA is, and this isdesirable. When the thickness t is great, it is desirable for the graindiameter d to be 150 nm or more from the viewpoint of processability.

As shown in FIG. 5C, when the thickness t of the transparent conductivefilm is small, the processability index PA is small and the residue issmall. When the thickness t is great, the processability index PA isgreat, that is, the residue is great. As shown in FIG. 5C, when thethickness t is 100 nm or less, the processability index PA is small, andthis is desirable. Furthermore, when the thickness t is 50 nm or less,the processability index PA is small, substantially 1, and a state whereresidue hardly occurs can be obtained. Here, it is difficult to visuallyinspect the degree of processing of a film having a thickness of 50 nmor less and thus, data of a stacked film in which transparent conductivefilms having the processability index of 1 and the grain diameter d of230 nm are stacked is shown.

The configuration of the embodiment is determined based on thecharacteristics found by the result of the experiment conducted by theinventors of the invention.

That is, the second average grain diameter d2 is smaller than the firstaverage grain diameter d1 and is 150 nm or less. Thus, a low contactresistance and high processability can be obtained. Specifically, it isdesirable for the second average grain diameter d2 to be 10 nm or moreand 150 nm or less. When the second average grain diameter d2 is lessthan 10 nm, the transmittance is reduced by scattering of light at thegrain boundary.

On the other hand, the first average grain diameter d1 is greater thanthe second average grain diameter d2. Thus, excellent processability canbe obtained. Specifically, the first average grain diameter d1 isgreater than 150 nm and 1 μm or less. When the first average graindiameter d1 exceeds 1 μm, for example, distortion is applied to thesecond conductive layer 52 and the contact resistance becomes high. Inparticular, it is desirable for the first average grain diameter d1 tobe greater than 150 nm and 500 nm or less. This makes it possible tomaintain high transmittance in the first conductive layer 51.Furthermore, high processability can be maintained.

From the result illustrated in FIG. 5C, the thickness of the secondconductive layer 52 is set to 100 nm or less. It is more desirable forthe thickness of the second conductive layer 52 to be 50 nm or less.Thus, still higher processability can be obtained. It is desirable forthe thickness of the second conductive layer 52 to be 1 nm or more.Thus, a low contact resistance can be obtained. If the thickness of thesecond conductive layer 52 is less than 1 nm, there may be a case wherethe contact resistance becomes high.

It is desirable for the thickness of the first conductive layer 51 to be50 nm or more and 400 nm or less. If the thickness of the firstconductive layer 51 is less than 50 nm, the resistance of thetransparent electrode 50 (the first conductive layer 51 and the secondconductive layer 52) becomes too high. If the thickness of the firstconductive layer 51 is greater than 400 nm, for example, the lightextraction efficiency becomes easily reduced.

Furthermore, by appropriately setting the thickness of the firstconductive layer 51 and the thickness of the second conductive layer 52to the above values, it is possible to reduce the volume resistivity ofthe transparent electrode 50 (the first conductive layer 51 and thesecond conductive layer 52). This allows more excellent electricalcharacteristics to be obtained.

In the transparent electrode 50, a phenomenon of interference of lightoccurs. Consequently, by adjusting the thickness (and the refractiveindex) of the transparent electrode 50, a high transmittance can beobtained.

The thickness t of the transparent electrode 50 is designed so that thetransmittance of light emitted to the top surface becomes maximum(reflectance becomes minimum). Hereinafter, the result of a simulationof a relationship between the thickness t, the refractive index, and thereflectance of the transparent electrode 50 will be described.

FIG. 6 is a graph illustrating the characteristics of the semiconductorlight emitting device according to the embodiment.

The horizontal axis of the graph represents the thickness t of thetransparent electrode 50. The vertical axis represents reflectance Rf.In the graph, the result of simulation of the reflectance Rf whenrefractive index n of the transparent electrode 50 is changed within therange of 1.90 to 2.20. In the simulation, the device structure is astacked structure of a p-type GaN layer, an ITO layer, a SiO₂ layer(refractive index n=1.45), a resin layer (refractive index n=1.4) andthe wavelength of light is set to 450 nm. That is, the configurationused in the simulation corresponds to a configuration in which a resinlayer is further provided on an insulating layer 60 (SiO₂ layer) in asemiconductor light emitting device 111, to be described later.

As shown in FIG. 6, the reflectance Rf changes depending on thethickness t and the refractive index n of the transparent electrode 50.The refractive index of ITO with a low resistivity is 1.9 or more and2.0 or less. Consequently, from FIG. 6, when ITO with a low resistivityis used as the transparent electrode 50, it is desirable to set thethickness t (sum of the thickness of the first conductive layer 51 andthe thickness of the second conductive layer 52) either to more than 150nm and 200 nm or less, or to 260 nm or more and 330 nm or less. Thisallows the low reflectance Rf to be obtained. That is, a hightransmittance can be obtained.

It is desirable to set the thickness of the second conductive layer 52either to a value more than 150 nm and 200 nm or less, which is thethickness t of the transparent electrode 50, minus the thickness of thefirst conductive layer 51, or to a value of 260 nm or more and 330 nm orless, which is the thickness t of the transparent electrode 50, minusthe thickness of the first conductive layer 51.

Thus, the optically excellent characteristics can be further obtained.

For example, as a first reference example, the configuration can besupposed for the transparent electrode 50, in which a stacked film of afilm by the vacuum evaporation method and a film by the spray thermaldecomposition method is used. This makes a film in which the graindiameters differ from one another to be formed. However, a layer by thevacuum evaporation method has a low density and low thermal durability.Therefore, the first reference example has a practical problem.

As a second reference example, the configuration can be supposed for thetransparent electrode 50, in which a stacked film of a film by thevacuum evaporation method and a film by the sputtering method is used.At this time also, the layer by the vacuum evaporation has a low densityand low thermal durability.

On the contrary to this, in the embodiment, the first conductive layer51 and the second conductive layer 52 are formed by the sputteringmethod. Then, by changing the conditions (for example, electric power)at the time of sputtering, the grain diameter of the first conductivelayer 51 is changed into the grain diameter of the second conductivelayer 52. Therefore, in the embodiment, the density of the film is highand the thermal durability is high. Furthermore, as described above, thegrain diameter (the second average grain diameter d2) of the secondconductive layer 52 is determined by the characteristics found by theinventors of the invention. This makes it possible to provide asemiconductor light emitting device having an electrode excellent in theelectrical characteristics and processability.

The film forming method of a transparent conductive film such as ITOincludes the electron beam evaporation method, the sputtering method,and the sol-gel method. According to the experiment of the inventors,when forming ITO with a low volume resistivity, the film formation bythe sputtering method is effective.

When forming an ITO film by sputtering, it is possible to obtain anamorphous ITO film by setting power low in film formation in anatmosphere substantially not including oxygen. This allows an ITO filmexcellent in processability to be obtained. However, in the amorphousITO film, there is a tendency for the contact resistance for the GaNlayer to become high. On the contrary, if power is high at the time offilm formation, the contact resistance becomes low, however,microcrystals are contained in the film, resulting in the cause ofresidue. That is, the processability is reduced.

In the embodiment, by appropriately setting the configuration of thefirst conductive layer 51 and the second conductive layer 52, highlyexcellent electrical characteristics and high processability areobtained at the same time.

In the embodiment, the second conductive layer 52 has a function toobtain excellent contact characteristics. When the second average graindiameter d2 of the second conductive layer 52 is small, the area ofclose adhesion with the second semiconductor layer 20 becomes large andthe resistance is reduced. It is desirable for the second average graindiameter d2 to be, for example, 10 nm or more and 50 nm or less. Thefirst conductive layer 51 has a function to reduce the resistance forenergization. It is desirable for the volume resistivity of the firstconductive layer 51 to be low. The greater the first average graindiameter d1, the less the grain boundary scattering becomes. Thus, theconductivity is increased. It is desirable for the first average graindiameter d1 of the first conductive layer 51 to be 300 nm or more and500 nm or less.

Hereinafter, an example of a method of manufacturing the semiconductorlight emitting device 110 will be described. The manufacturing method isa method of manufacturing a semiconductor light emitting deviceincluding the first semiconductor layer 10 of the first conductivitytype, the second semiconductor layer 20 of the second conductivity type,the light emitting part 30 provided between the first semiconductorlayer 10 and the second semiconductor layer 20, the first conductivelayer 51 which includes a polycrystal having the first average graindiameter d1 and is transparent to light emitted from the light emittingpart 30, and the second conductive layer 52 which is in contact with thesecond semiconductor layer 20 and the first conductive layer 51 betweenthe second semiconductor layer 20 and the first conductive layer 51,includes a polycrystal having the second average grain diameter d2smaller than the first average grain diameter d1, and is transparent tothe above-mentioned light.

FIG. 7 is a flowchart illustrating the method of manufacturing thesemiconductor light emitting device according to the embodiment.

FIGS. 8A to 8C are schematic sectional views in order of process,illustrating the method of manufacturing the semiconductor lightemitting device according to the embodiment.

As shown in FIG. 7 and FIG. 8A, a first film f1, which forms the secondconductive layer 52, is formed on the second semiconductor layer 20 inan atmosphere of a noble gas by the sputtering method using firstelectric power (step S110). That is, in an Ar atmosphere, an amorphousITO film including a comparatively large amount of microcrystal isformed. Here, the concentration of oxygen during the period of filmformation is adjusted so that the composition of the ITO film becomesoxygen-deficient.

As shown in FIG. 7 and FIG. 8B, a second film f2, which forms the firstconductive layer 51, is formed on the first film f1 in an atmosphere ofa noble gas by the sputtering method using second electric power smallerthan the first electric power (step S120). For example, the formedsecond film f2 is amorphous. That is, after reducing the power at thetime of sputtering, an amorphous ITO film having a comparatively smallamount of microcrystal is formed in an Ar atmosphere.

Meanwhile, not limited to the above, when forming the first film f1 andthe second film f2, a target including an oxide including at least oneof elements selected from the group consisting of, for example, In, Sn,Zn, and Ti is used. The first film f1 and the second film f2 formed bysputtering include an oxide including at least one of elements selectedfrom the group of In, Sn, Zn, and Ti.

The formation of the first film f1 and the formation of the second filmf2 are performed in an atmosphere substantially not including oxygen.That is, the first film f1 and the second film f2 are films including anoxygen-deficient transparent conductive oxide.

Here, it is desirable for sum of the thickness of the first film f1 andthe thickness of the second film f2 to be one of larger than 150 nm and200 nm or less, and 260 nm or more and 330 nm or less. Thus, the lowreflectance Rf is obtained. That is, the high transmittance is obtained.

As shown in FIG. 7 and FIG. 8C, the first conductive layer 51 and thesecond conductive layer 52 are formed by subjecting the first film f1and the second film f2 to heat treatment in an atmosphere includingoxygen (step S140). The second average grain diameter of the secondconductive layer 52 is, for example, 150 nm or less.

By subjecting the first film f1 and the second film f2 to heat treatmentin an oxidizing atmosphere, oxygen is taken in the film. This causes acrystal grow. Therefore, from the first film f1, the polycrystallinesecond conductive layer 52 having a grain diameter (the second averagegrain diameter d2) of, for example, 10 nm or more and 150 nm or less isobtained. Then, from the second film f2, the polycrystalline firstconductive layer 51 having a grain diameter (the first average graindiameter d1) of more than 150 nm and 1 μm or less is obtained.

This makes it possible to manufacture a semiconductor light emittingdevice having an electrode excellent in electrical characteristics andprocessability.

As shown in FIG. 7, it may also be possible to further perform a processof processing the first film f1 and the second film f2 into apredetermined shape (step S130). That is, the manufacturing method canfurther include a process of processing the first film f1 and the secondfilm f2 into a predetermined shape (step S130) between the formation ofthe second film f1 (step S120) and the above-mentioned heat treatment(step S140).

Before heat treatment, the second film f2 is amorphous, and thus, theprocessability is comparatively high. Furthermore, even though the firstfilm f1 is polycrystalline, the thickness of the first film f1 iscomparatively small, and thus, the processability is comparatively high.After that, by forming the second conductive layer 52 and the firstconductive layer 51, respectively, from the first film f1 and the secondfilm f2 by heat treatment, highly excellent electrical characteristicsand high processability are obtained at the same time.

Furthermore, as shown in FIG. 7, the manufacturing method can furtherinclude a process of further subjecting the first film f1 (the secondconductive layer 52) and the second film f2 (the first conductive layer51) to heat treatment in a reduction atmosphere (step S150) after theheat treatment in an atmosphere including oxygen (step S140).

This makes it possible to remove excess oxygen included in the secondconductive layer 52 and the first conductive layer 51. That is, it ispossible to obtain an ITO film with a desired volume resistivity byseparating excess oxygen from the film by sinter processing in areduction atmosphere.

As described above, in the embodiment, first, an ITO thin film includinga comparatively large amount of microcrystal is formed by sputtering onthe p-type GaN layer. Thus, excellent contact characteristics with thep-type GaN layer are obtained. After this, the power of sputtering isreduced and an ITO thin film including a comparatively small amount ofmicrocrystal is formed in an Ar atmosphere. This film is an amorphousfilm, and thus, processability is excellent. After that, by subjectingthese films to sinter processing in an atmosphere including oxygen, theychange into a polycrystalline film having a crystal grain diameter of 10nm or more and 150 nm or less and a polycrystalline film having acrystal grain diameter of more than 150 nm and 500 nm or less. By usingthe structure and process, it becomes possible to obtain a low contactresistance and high processability at the same time.

FIG. 9 is a schematic sectional view illustrating the configuration ofanother semiconductor light emitting device according to the embodiment.

As shown in FIG. 9, the other semiconductor light emitting device 111according to the embodiment further includes the insulating layer 60.The first conductive layer 51 is provided between the insulating layer60 and the second conductive layer 52. The insulating layer 60 istransparent to emission light. As the insulating layer 60, for example,a silicon oxide film is used. The embodiment is not limited to this andas the insulating layer 60, an arbitrary insulating material beingtransparent to light emitted from the light emitting part 30 can beused.

The insulating layer 60 is provided at a part other than the part wherethe first conductive layer 51 is in contact with the second electrode80. This secures electrical conduction between the first conductivelayer 51 and the second electrode 80.

The insulating layer 60 covers, for example, the side surfaces of thefirst conductive layer 51, the second conductive layer 52, the secondsemiconductor layer 20, and the light emitting part 30. Furthermore, theinsulating layer 60 is provided on the side surface of the firstsemiconductor layer 10 and the surface of the first semiconductor layer10 on the side of the first major surface 10 a. The insulating layer 60functions as a passivation film of the stacked structure body 10 s. Theinsulating layer 60 is provided at a part other than the part where thefirst semiconductor layer 10 is in contact with the first electrode 70.This secures the electrical conduction between the first semiconductorlayer 10 and the first electrode 70.

The insulating layer 60 may be provided as necessary or may be omitted.

In the semiconductor light emitting device 111 also, the secondconductive layer 52 includes a polycrystal having the second averagegrain diameter d2 of 150 nm or less, which is smaller than the firstaverage grain diameter d1. This makes it possible to provide asemiconductor light emitting device having an electrode with excellentelectrical characteristics and processability.

FIG. 10 is a schematic sectional view illustrating the configuration ofanother semiconductor light emitting device according to the embodiment.As shown in FIG. 10, another semiconductor light emitting device 112according to the embodiment further includes a third conductive layer 53in addition to the first semiconductor layer 10, the secondsemiconductor layer 20, the light emitting part 30, the first conductivelayer 51, and the second conductive layer 52.

The transmittance to the above-mentioned light in the third conductivelayer 53 is lower than the transmittance of the first conductive layer51 and lower than the transmittance of the second conductive layer 52.As the third conductive layer 53, for example, a metal layer is used.The third conductive layer 53 is, for example, the second electrode 80.As the third conductive layer 53, for example, a stacked film of a Nifilm and an Au film is used.

The first conductive layer 51 has a first portion 51 p and a secondportion 51 q. The first portion 51 p is in contact with the thirdconductive layer 53 and the second semiconductor layer 20 between thethird conductive layer 53 and the second semiconductor layer 20. Thesecond portion 51 q is not covered with the third conductive layer 53and covers at least a part of the second conductive layer 52.

The contact resistance between the first conductive layer 51 and thesecond semiconductor layer 20 is higher than the contact resistancebetween the second conductive layer 52 and the second semiconductorlayer 20. Thus, the contact resistance at the first portion 51 p of thefirst conductive layer 51, which is in contact with the secondsemiconductor layer 20, is high. Therefore, light emission at the lightemitting part 30 corresponding to the first portion 51 p is suppressed.That is, light emission at the second portion 51 q where the contactresistance is low is promoted.

That is, light emission at the first portion 51 p corresponding to thethird conductive layer 53 having a lower transmittance (having lightshielding or reflecting property) is suppressed. Thus, the lightextraction efficiency is improved.

In the semiconductor light emitting device 112 also, the secondconductive layer 52 includes a polycrystal having the second averagegrain diameter d2 of 150 nm or less, which is smaller than the firstaverage grain diameter d1. This makes it possible to provide asemiconductor light emitting device having an electrode with excellentelectrical characteristics and processability.

According to the embodiment, a semiconductor light emitting devicehaving an electrode excellent in electrical characteristics andprocessability and a method of manufacturing the same are provided.

In the specification, “nitride semiconductor” includes all compositionsof semiconductors of the chemical formula B_(x)In_(y)Al_(z)Ga_(1-x-y-z)N(0≦x≦1, 0≦y≦1, 0≦z≦1, and x+y+z≦1) for which each of the compositionalproportions x, y, and z are changed within the ranges. “Nitridesemiconductor” further includes group V elements other than N (nitrogen)in the chemical formula recited above, various elements added to controlvarious properties such as the conductivity type, etc., and variouselements included unintentionally.

In the specification of the application, “perpendicular” and “parallel”refer to not only strictly perpendicular and strictly parallel but alsoinclude, for example, the fluctuation because of manufacturingprocesses, etc. and “substantially perpendicular” and “substantiallyparallel” will suffice.

Hereinabove, exemplary embodiments of the invention are described withreference to specific examples. However, the invention is not limited tothese specific examples. For example, one skilled in the art maysimilarly practice the invention by appropriately selecting specificconfigurations of components included in semiconductor light emittingdevices such as semiconductor layers, n-type semiconductor layers,p-type semiconductor layers, light emitting parts, transparent electrodelayers, electrodes, etc., from the known art. Such practice is includedin the scope of the invention to the extent that similar effects theretoare obtained.

Furthermore, any two or more components of the specific examples may becombined within the extent of technical feasibility and are included inthe scope of the invention to the extent that the purport of theinvention is included.

Moreover, all semiconductor light emitting devices and methods ofmanufacturing the same practicable by an appropriate design modificationby one skilled in the art based on the semiconductor light emittingdevices and the methods of manufacturing the same described above asembodiments of the invention also are within the scope of the inventionto the extent that the purport of the embodiments of the invention isincluded.

Various other variations and modifications can be conceived by thoseskilled in the art within the spirit of the invention, and it isunderstood that such variations and modifications are also encompassedwithin the scope of the invention.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A semiconductor light emitting device comprising:a first conductive layer; a first semiconductor layer of a firstconductivity type; a second semiconductor layer of a second conductivitytype, the second semiconductor layer being provided between the firstconductive layer and the first semiconductor layer; a light emittingpart provided between the first semiconductor layer and the secondsemiconductor layer; and a second conductive layer being in contact withthe second semiconductor layer and the first conductive layer, thesecond conductive layer being provided between the second semiconductorlayer and the first conductive layer, the first conductive layerincluding a polycrystal having a first average grain diameter, the firstconductive layer being transmittable with respect to light emitted fromthe light emitting part, and the second conductive layer including apolycrystal having a second average grain diameter of 150 nanometers orless, the second average grain diameter being smaller than the firstaverage grain diameter, and the second conductive layer beingtransmittable with respect to the light.
 2. The device according toclaim 1, wherein a thickness of the second conductive layer is 100nanometers or less.
 3. The device according to claim 1, wherein sum of athickness of the first conductive layer and the thickness of the secondconductive layer is one of more than 150 nanometers and 200 nanometersor less and 260 nanometers or more and 330 nanometers or less.
 4. Thedevice according to claim 1, wherein the first conductive layer and thesecond conductive layer include an oxide including at least one ofelements selected from the group of In, Sn, Zn, and Ti.
 5. The deviceaccording to claim 1, further comprising a third conductive layer havingtransmittance to the light lower than transmittance of the firstconductive layer and lower than transmittance of the second conductivelayer, the first conductive layer having: a first portion being incontact with the third conductive layer and the second semiconductorlayer between the third conductive layer and the second semiconductorlayer; and a second portion being not covered with the third conductivelayer and covering at least a part of the second conductive layer. 6.The device according to claim 5, wherein the third conductive layer is ametal layer.
 7. The device according to claim 1, wherein a thickness ofthe second conductive layer is less than a thickness of the firstconductive layer.
 8. The device according to claim 1, wherein athickness of the second conductive layer is 50 nanometers or less. 9.The device according to claim 1, wherein a thickness of the firstconductive layer is 50 nanometers or more and 400 nanometers or less.10. The device according to claim 1, wherein the first average graindiameter is 150 nanometers or more and 1 micrometers or less.
 11. Thedevice according to claim 1, wherein the second average grain diameteris 10 nanometers or more.
 12. A method of manufacturing a semiconductorlight emitting device including a first conductive layer, a firstsemiconductor layer of a first conductivity type, a second semiconductorlayer of a second conductivity type, the second semiconductor layerbeing provided between the first conductive layer and the firstsemiconductor layer, a light emitting part provided between the firstsemiconductor layer and the second semiconductor layer, the methodcomprising: forming a first film on the second semiconductor layer in anatmosphere of a noble gas by a sputtering method using a first electricpower, the first film being transmittable with respect to light emittedfrom the light emitting part; forming a second film on the first film inan atmosphere of a noble gas by the sputtering method using a secondelectric power smaller than the first electric power, the second filmbeing transmittable with respect to light emitted from the lightemitting part; and subjecting the first film and the second film to aheat treatment in an atmosphere including oxygen; and wherein the firstconductive layer made of the second film after the subjecting includes apolycrystal having a first average grain diameter, a second conductivelayer made of the first film after the subjecting includes a polycrystalhaving a second average grain diameter, and the second average graindiameter is smaller than the first average grain diameter.
 13. Themethod according to claim 12, wherein the first film and the second filmare processed into a predetermined shape between the forming the secondfilm and the heat treatment.
 14. The method according to claim 12,wherein the forming the first film and the forming the second film areperformed in an atmosphere not including oxygen.
 15. The methodaccording to claim 12, wherein after the heat treatment in theatmosphere including oxygen, the first film and the second film arefurther subjected to heat treatment in a reduction atmosphere.
 16. Themethod according to claim 12, wherein the second film is amorphous. 17.The method according to claim 12, wherein the second average graindiameter is 150 nanometers or less.
 18. The method according to claim12, wherein the first average grain diameter is 150 nanometers or moreand 1 micrometers or less.
 19. The method according to claim 12, whereinsum of a thickness of the first film and the thickness of the secondfilm is one of more than 150 nanometers and 200 nanometers or less and260 nanometers or more and 330 nanometers or less.
 20. The methodaccording to claim 12, wherein the forming the first film and theforming the second film include performing sputtering using a targetincluding an oxide including at least one of elements selected from thegroup of In, Sn, Zn and Ti.
 21. The device according to claim 1, whereinthe first semiconductor layer includes a nitride semiconductor and thesecond semiconductor layer includes a nitride semiconductor.
 22. Thedevice according to claim 1, a first distance between first grainboundaries in the first conductive layer is greater than a seconddistance between second grain boundaries in the second conductive layer.